Through Swiss Pat. No. 527,935 (corresponding to U.S. Pat. No.3,759,298), such a dobby for controlling weaving machines has become known. By additively coupling the control effects of the two heddle frame lifting units in the transmitting drive train, a rocking lever can be moved into four operating positions. If the heddle frame connecting rod is hinged to the rocking lever at the point of intersection of two positions of the rocking lever, two of the operating positions of the heddle frame will be identical. In other words, only three different heddle frame positions are then obtained.
Such power-transmitting drives are subjected to usually heavy stresses because the particularly heavy heddle frame of a weaving machine for plush fabrics must be moved at high speed over almost twice the shed-lifting path as the heddle frame of a weaving machine for smooth fabrics.
The pile threads which are controlled with such heddle frames are usually filaments which are not twisted or are only weakly twisted and thus have a tendency to break under the influence of unusual heddle frame vibrations. Such vibrations do occur, particularly due to elastic deformations of the alternately loaded bearing shafts for the reciprocating levers and through the series of bearing points and hinge points of connecting bars and rods in the path of movement of the power-transmitting drive.
These uncontrolled, wild vibrations, which in simple machines are insignificant, add up in the drive between lifting units and heddle frame of machines for plush fabrics, which leads to additional vibrations of the heddle frames and thus to breaking of the pile threads.
A purpose of the invention is thus, as much as possible, to provide a dobby which reduces the wild, vibration like movements of the heddle frame.